Description. (in parentheses the data of the holotype) Shell small for the genus, height
4.85–5.1 (5.1 mm), width 2.45–2.75 (2.75 mm), solid, fusiform, biconic, stout, H/W=1.854–2.000 (1.854). Protoconch paucispiral shiny, of 1.25–1.3 (1.3) slightly convex whorl (last 0.25 whorl almost flat), d 0.20–0.24 (0.20 mm), Do 0.35–0.40 (0.40 mm), DM 0.50–0.55 (0.55 mm), h 0.40–0.45 (0.45 mm), sculptured by sparse rare microgranules. Protoconch-teleoconch boundary well marked, barely flexuose, opisthocline. Teleoconch of da 3.8–4.1 (4.1) slightly convex whorls. Sculpture starting with 3 (3) weak spiral cordlets crossed by 18 (18) opisthocline axial ribs on the first whorl. Additional spiral cordlets between the adapical ones and between the suprasutural one and the suture. Last whorl sculptured over the entire surface by 18–19 (18) scarcely pronounced spiral cordlets, flat, equidistant, of equal size, but weaker on the periphery, as broad as three times the interspaces, of which 4–5 (4) above the aperture. Axial ribs present only on the first three whorls producing nodules at the intersection with the spirals. Two strong columellar folds, the posterior slightly bifid on its outer tip. Weak growth lines visible over the entire surface. Outer lip sharp, thickened internally with four pairs of denticles barely elongated, the posterior pair more pronounced. Anal sinus barely visible. Siphonal canal short, and wide. Coloration dark brown in the background (including the protoconch), with sparse lighter blurs. The columellar folds and the inner side of the outer lip lighter brown. Soft parts white with black eyes.

M. mifsudi n. sp. is characterized by the small size, the flat spiral cords and the low ratio H/W (1.854–2.000). M. mariottinii has more pronounced and more spaced apart sculpture, and a different coloration with a brown background, the suprasutural cord with white blotches, and the two adapical ones (sometimes only the most adapical) darker; furthermore it is generally more slender (H/W 2.000–2.321). See under M. tricolorata for the differences with this species.

Type locality. Caprera Is., Maddalena Archipelago, Sardinia. Known only from the type locality, in the western Tyrrhenina Sea. Recent. Live specimens under rocks without algal covering, in 0.25 m water. Found sympatric, often at different depths, with M. karpathoensis.